[amsat-bb] Re: Since We Are Off Topic Somewhat....

[Bruce Bostwick]

The *energy* is exactly the same, the sole exception being whatever  
little bits of delta-V were added or subtracted by OMS burns.  I  
emphasize *energy* because the acceleration/deceleration is a change  
in energy that can be thought of as a form of power or work, both of  
which have a differential/integral relationship to energy.  And it's  
that differential/integral relationship that supplies all the wiggle  
room in this problem, because you can't control how *much* kinetic  
energy you're getting rid of, but you can control how you spread out  
that energy dispersal over time, to some extent.

An extremely accurate analogy is driving your car down a back country  
road and seeing the railroad crossing ahead light up and the gates  
start to close -- your initial speed is the same no matter what you  
do, but you can choose to drive all the way up to the crossing and try  
to stop as hard as you can right there, which will send everything in  
the car flying and probably set your brakes on fire or raise a cloud  
of smoke from your tires, or you can choose to put a light pressure on  
the brake and gradually slow down until you finally stop at the  
crossing, and barely feel the deceleration and maybe only slightly  
warm up your brakes.  Same initial kinetic energy, vastly different  
dispersal rates.  :D

On Feb 15, 2008, at 3:36 AM, Auke de Jong, VE6PWN wrote:

> This might be excessively basic, but wouldn't the heat energy of the
> friction in re-entry be roughly equivalent to the energy from the  
> engines
> which put the craft up there in the first place?  This doesn't  
> include the
> de-orbit burn, obviously, but since the shuttle has a lot of mass,  
> there
> will be more time spent at high velocity dragging against the  
> atmosphere,
> than a relatively small satellite which weighs much less mass, given  
> the
> same descent path because of it's higher intertia(Kinetic Energy).

"This is an amazing honor. I want you to know that I spend so much  
time in the world that is spinning all the time, that to be in the no- 
spin zone actually gives me vertigo." -- Stephen Colbert during an  
interview on FOX News, The O'Reilly Factor